Annual epidemics of seasonal influenza cause substantial morbidity and mortality in the US with high rates of hospitalizations, emergency department and outpatient visits, and medical costs. Children experience significant morbidity from influenza, and also play a critical role in spreading infection to adults. Since 2010, the Advisory Committee on Immunization Practices (ACIP) has recommended influenza vaccination for all children >6 months of age. However, vaccination rates remain very low-- only 56% of children 2-17 years are vaccinated. Low rates are a concern for both seasonal influenza and in preparation for pandemic influenza. One of the nationally recommended strategies for raising childhood influenza vaccination rates is to use parent reminder/recall (R/R) by phone or mail, which can raise rates by up to 20 percentage points. However, less than 16% of primary care practices use R/R despite many studies showing its effectiveness. Statewide immunization information systems (IISs) now exist in all states to track childhood vaccinations, but they have not been used for R/R for influenza vaccine because of the lack of evidence for its effectiveness and lack of a template for IIS-based R/R. We have united two leading immunization research groups (Denver, CO and Rochester, NY) to assess the impact of centralized IIS-based influenza vaccine R/R, and to evaluate the added value of mailed R/R over the less-expensive phone R/R. We will also develop tools to aid other states in creating efficient IIS R/R systems for seasonal and possible pandemic influenza outbreaks. Our study has four aims. Aim 1 is to develop the protocols, clinical decision support, and message content for state IISs to conduct reminder/recall for influenza vaccinations. Aim 2a is to compare centralized IIS autodialer (phone) R/R to standard of care control to assess the impact of IIS R/R on vaccination rates. We will use a cluster- randomized pragmatic trial in two states (CO and NY) that vary in vaccination delivery systems and will apply the RE-AIM framework to evaluate the reach, effectiveness/cost-effectiveness, adoption and implementation of IIS R/R. This RCT will involve 66,000 children 6m-17yrs from 60 practices, allowing us to assess the impact of IIS R/R on the entire population and on subgroups. Aim 2b will use a nested RCT within the above RCT to compare the impact of IIS-based R/R to the child's practice versus IIS-based R/R to the practice plus other community vaccination sites Aim 3 will evaluate the added benefit (and costs) of mailed R/R for autodialer failures (wrong number, no phone). For this aim we will use a 2-arm RCT, randomizing children within practices to autodialer-alone versus combined autodialer + mailed R/R. This RCT will involve 33,000 children from 60 practices. Aim 4 (dissemination aim) will develop a toolkit for state IIS-based influenza vaccine R/R for seasonal and pandemic influenza, and work with key stakeholders on a sustainability plan. By the end of the study we will have a feasible and cost-effective model to raise child seasonal or possibly pandemic influenza vaccination rates to prevent influenza. We will disseminate the IIS model to all states.